What are the symptoms and treatment options for hypothermia, particularly in patients with underlying medical conditions such as diabetes or cardiovascular disease?

Symptoms of Hypothermia

Hypothermia presents with a progressive spectrum of symptoms that correlate with core body temperature, ranging from shivering and confusion in mild cases to coma and cardiac arrest in severe cases, requiring immediate recognition and temperature-based treatment rather than relying on clinical presentation alone.

Classification and Temperature Thresholds

Hypothermia is defined as a core body temperature below 35°C (95°F) and is classified into distinct severity categories 1, 2:

• Mild hypothermia: 34-35°C (93.2-95°F)
• Moderate hypothermia: 30-34°C (86-93.2°F)
• Severe hypothermia: <30°C (<86°F)
• Profound hypothermia: <24°C (<75.2°F)

Critical caveat: Clinical presentation may not correlate with core temperature severity. A rare case documented a patient with severe hypothermia (25.1°C) who remained alert and communicative, demonstrating that diagnosis and treatment must always be based on measured core body temperature using a low-reading thermometer rather than clinical symptoms alone 2.

Progressive Symptom Presentation by Severity

Mild Hypothermia (34-35°C)

• Shivering (increases metabolic heat production) 3
• Confusion and impaired coordination 3
• Somnolence 3
• Tachycardia and tachypnea (early compensatory response) 2
• Elevated blood pressure 2
• Increased systemic vascular resistance 3

Moderate Hypothermia (30-34°C)

• Progression to coma occurs at approximately 30°C 3
• Bradycardia develops (which may paradoxically be beneficial, similar to beta-blocker effects) 3
• Decreased cardiac output 4
• Cold-induced diuresis initially, followed by decreased glomerular filtration rate 3, 4
• Atrial fibrillation may develop 2
• Decreased minute ventilation as the medullary respiratory center becomes depressed at 32°C 3

Severe Hypothermia (<30°C)

• Loss of deep tendon reflexes and pupillary reflexes below 27°C 3
• Profound central nervous system depression 2
• Severe slowing of vital signs 2
• Comatose status 2
• Cardiac arrest risk increases significantly 5
• Pulse and respiratory rates may be slow or difficult to detect 5

Metabolic and Systemic Effects

Cardiovascular Manifestations

• Bradycardia (heart rate slows progressively with temperature decline) 5, 3
• Increased systemic vascular resistance consistently occurs with mild hypothermia 3
• Myocardial contractility typically increases in most patients initially 3
• Progressive depression of cardiac activity in moderate to severe hypothermia 3
• Arrhythmias (usually bradycardia, but risk of clinically significant arrhythmias only below 30°C) 5, 6

Metabolic Derangements

• Hyperglycemia due to decreased insulin sensitivity and insulin secretion 5, 3
• Increased blood glucose variability during hypothermia (associated with worse outcomes) 7
• Electrolyte abnormalities: hypophosphatemia, hypokalemia, hypomagnesemia, and hypocalcemia 5, 3
• Decreased metabolic rate: cerebral metabolism decreases by approximately 6-7% for each 1°C reduction in core temperature 3

Hematological Effects

• Impaired platelet function between 33-37°C 3
• Impaired coagulation factor activity below 33°C 3, 4
• Thrombocytopenia (though not typically associated with increased bleeding clinically) 5

Renal and Fluid Balance

• Cold-induced diuresis initially 3, 4
• Decreased glomerular filtration rate with prolonged cooling 3, 4
• Dehydration and electrolyte disturbances that further compromise organ function 3

Infectious Complications

• Impaired immune system function 5, 3
• Increased infection rates, particularly pneumonia 5, 3
• Increased respiratory tract infections 6

Neurological Effects

• Decreased clearance of sedative drugs and neuromuscular blockers by up to 30% at 34°C 5, 3
• Progressive central nervous system depression correlating with temperature decline 3, 2

Special Considerations for Patients with Underlying Conditions

Diabetes

Patients with diabetes face compounded risks during hypothermia 3:

• Impaired thermoregulation from hypoglycemia 4
• Exacerbated hyperglycemia from hypothermia-induced insulin resistance 5, 3
• Greater insulin requirements during hypothermic states 7
• Increased blood glucose variability (independent predictor of mortality) 7

Cardiovascular Disease

Patients with cardiovascular disease experience heightened vulnerability 3:

• Dehydration and electrolyte disturbances from cold-induced diuresis particularly compromise cardiac function 3
• Increased systemic vascular resistance places additional strain on compromised hearts 3, 4
• Bradycardia and decreased cardiac output may precipitate decompensation 4
• Diastolic dysfunction may develop in some patients despite generally increased contractility 6

Treatment Approach Based on Severity

Mild Hypothermia (>34°C)

• Passive rewarming is generally adequate 5
• Remove wet garments and insulate from further environmental exposure 5
• Move to warm environment 1

Moderate Hypothermia (30-34°C)

• External warming techniques are appropriate 5
• Active external rewarming including forced air or efficient surface-warming devices 5
• Passive rewarming alone is inadequate 5

Severe Hypothermia (<30°C)

• Core rewarming is required 5
• Cardiopulmonary bypass provides most rapid rewarming for patients in cardiac arrest 5, 8
• Alternative core rewarming techniques: warm-water lavage of thoracic cavity, extracorporeal blood warming 5
• Adjunctive measures: warmed IV/IO fluids, warm humidified oxygen (supplementary only) 5
• Do not delay urgent procedures (airway management, vascular access) despite cardiac irritability concerns 5

Critical Resuscitation Principles

For hypothermic cardiac arrest, victims should not be considered dead before rewarming unless obvious signs of death (rigor mortis, decomposition, decapitation) are present 8:

• Continue CPR until rewarmed to ≥32-34°C 8
• Defibrillation attempts should continue per standard algorithms, though success unlikely until core temperature reaches 30-34°C 8
• Transport to ECLS-capable facility should be prioritized 8
• Do not stop resuscitation until successfully rewarmed to normothermia and remains in refractory arrest despite appropriate interventions 8

Key Clinical Pitfalls

• Never rely on clinical presentation alone to determine hypothermia severity—always measure core temperature with low-reading thermometer 2
• Do not delay transport to ECMO-capable center for prolonged field resuscitation in severe cases 8
• Monitor and aggressively correct electrolyte abnormalities, especially during induction and rewarming phases 5
• Rewarm slowly at approximately 0.25-0.5°C per hour to avoid rebound hyperthermia (associated with worse outcomes) 5, 3
• Recognize that shivering in hypothermic patients is a normal physiological response associated with good outcomes 5, 3